The present invention lies in the field of well drilling.
It more particularly relates to a radially expandable metal tubular element having on its outer surface a series of spaced apart, annular sealing modules.
The invention also concerns a device to isolate part of a wellbore comprising a pipe provided on a section of its outer surface with at least one of the aforementioned expandable tubular elements.
Finally the invention concerns a method for the sealed applying of the aforementioned isolating device against the wall of a wellbore or casing placed inside this wellbore.
The invention can be applied to the tubing of a vertical or horizontal wellbore.
This second wellbore configuration has been given more general use in recent years further to new extraction techniques and in particular, but not limited thereto, hydraulic fracturing techniques.
The operating of wellbores, whether vertical or horizontal, requires the sealing of some regions of the wellbore in relation to others, for example to delimit an area inside which it will later be possible to conduct operations.
To illustrate the state of the art in the matter appended FIGS. 1 and 2 illustrate a fraction of a metal tubular pipe known as a “base pipe” BP or casing, which is placed in position inside a well and more particularly in the horizontal part thereof.
In practice this base pipe BP also comprises a vertical upstream end which leads into the surface of the wellbore, and a curved intermediate portion to connect the vertical part with the horizontal part (these not being illustrated for reasons of simplification).
It is a tubular pipe formed of several sections placed end to end so as to form a completion.
In the two aforementioned Figures, the pipe BP is positioned in an open wellbore A whose surface is as drilled.
However it can easily be envisaged that A designates a metal tube (casing) in which it is intended to conduct operations.
Against the outer surface of this base pipe BP and on a portion thereof there extends a cylindrical or approximately cylindrical jacket C whose opposite ends are sealingly secured to the outer surface of the pipe, for example via rings B. This jacket is preferably in metal.
At least one opening O is arranged in the wall of the base pipe BP to cause its inner space to communicate with the annular space arranged between the wall of the base pipe BP and the jacket C.
In the appended Figures only one opening O is illustrated. However it is possible to have a higher number of openings e.g. four or six.
Still as known per se the jacket C is covered over all or part of its length with a layer of elastically deformable material e.g. elastomer which forms an annular sealing «web» D a few millimeters thick.
In FIG. 1 the jacket C is shown in its initial state, namely its wall is not yet deformed. At this stage it is globally cylindrical. The wellbore is at absolute pressure P0.
As shown in FIG. 2, sufficient fluid pressure P1 is applied (preferably a liquid such as water) inside the base pipe BP. This pressure, via the openings O, is communicated inside the jacket C which expands radially beyond its elastic deformation limit.
By so doing the web D of elastomer material comes into contact with the inner wall A of the wellbore or casing.
By then applying an overpressure ΔP, so that the overall pressure becomes P1+□P, the sealing web D is compressed against the wall thereby sealingly isolating the annular spaces EA1 and EA2 arranged either side of the jacket C.
When the pressure is lowered inside the base pipe BP for return to initial pressure P0, the diameter of the jacket C tends to reduce slightly on account of elastic return. This geometric modification must be offset by the sealing layer D to maintain proper isolation between the aforementioned annular spaces.
The reference Z in FIG. 2 designates a zone which is magnified in appended FIGS. 3 and 4.
FIG. 3 illustrates the device during expansion of the jacket whilst FIG. 4 shows the device after release of the expansion pressure. Since the elastomer of the web D is relatively little compressible, it is only scarcely compressed even after the application of strong overpressure and contact with the wall of the wellbore A.
This overpressure may be in the order of 50 to 100 bars.
After release of the pressure (return to initial pressure P0) and hence after elastic return of the jacket C, it is then possible that there is no longer any contact between the inner wall of the wellbore and the web of material D, thereby leaving a communication space j between the aforementioned annular spaces EA1 and EA2.
Under these conditions no satisfactory seal is obtained.
It has also been proposed not to use a continuous web D of sealing material but a series of annular sealing strips spaced apart as described in document U.S. Pat. No. 6,640,893 and illustrated in appended FIG. 5.
When considering the cross-section of these sealing strips E it can be seen that they are separated from one another by annular spaces F.
Most of the time the jacket C is expanded even though the well is filled with water which means that this liquid is trapped between the sealing strips in the spaces F.
This liquid being scarcely compressible, the pressure □P is trapped between the sealing strips E and the fluid can no longer be evacuated.
The same phenomenon of defective sealing is then observed as described above in connection with FIGS. 3 and 4, since the elastomer is not able to be sufficiently compressed and is unable to offset elastic return.
Other techniques for deforming an expandable jacket have been proposed.
For example document U.S. Pat. No. 7,370,708 describes a device comprising not a sealing layer in elastomer but metal lips directly secured to the expandable jacket.
On expansion of the jacket which is obtained using a mandrel sliding longitudinally, these lips are plastically deformed in turn against the wall. The low elastic return of these lips is not sufficient to offset the elastic return and reduction in diameter of the actual jacket, which leaves a communication space between the two annular spaces EA1 and EA2.
Also, document U.S. Pat. No. 7,070,001 relates to sealing lips secured to an expandable jacket and parallel to the axis thereof. These are coupled to sealing layers in inflatable elastomer.
The described jacket is deformed by a rotating tool system with rollers.
It will be noted that the two above-mentioned devices do not allow an annular isolating device to be obtained wherein an expandable jacket C is arranged around a base pipe BP.